Controlling mechanism for alternating-current motors



July 27 1926. 1,593,659

R. G. STANDERWICK CONTROLLING MECHANISM FOR ALIERNATING CURRENT MOTORS Filed July 30, 1925 Fig. l

Inventor.

J QLncLLd G. StanderwLck,

HLs Attorney.

Patented July 27, 1926.

nnomnn e. s'rannnnwrcx, or xmmnan, mssacnusn'r'rs, asaronon 'ro Guam ELECTRIC GOIPANY,

A CORPORATION OI YORK,

QI'IBOLLING IECHANISI FOB ALTERNATING-OUWT IOTOBB.

Application fled ialy 80,

The present invention relates to controlling mechanism for alternating current motors. Y

The primary object of the invention is to 6 provide roved controlling mechanism whereby an ternating current motor may be reversed as to direction of rotation and run satisfactorily in both directions without the making or breaking of any contacts.

10 A further object of my invention is to provide a controllin mechanism which, while accomplishing-t e object set iorth in the preceding paragraph, at the same time will give. a sensitive adjustment of speed 15 and rat ire but small movements in e ectin s'uc adjustments. v

For a consideration ofwhat I believe to be novel and my invention, attention isdirected to the accom anying description and 20 the claims appended thereto.

In the drawing, Fig. 1"is a diagrammatic yiew of a construction embodying my inven-' tion; Fig. 2 is a detail sectional view of certain parts; Fig. 3 is a wiring diagram; and

as. Fig. 4 shows an application of the invention wherein it is utilized to control the speed of an elastic fluid turbine.

' Referring to the drawing, 5 indicates the armature and 6 the field winding of an alternating current motor. It may be an alternating current motor of any suitable type wherein the direction of rotation is reversed by-reversing the direction of flow of the currents in the armature and field g relatively to each other, this being accomplished referably by reversin the direction of ow oi the currents in t e armature ,relatively to those in the field. For example, a universally wound motor may be 40. utilized. 7 and 8 indicate the two line-wires of a suitable supply of alternatin current, Lfield winding 6 bein connecte directly across the line by con uctors 9 and 10.

For controllingl the direction of flow' of Q the currents in t e armature winding relatively to those in the field winding, I provide two sets of coils 11 and 12, each set comprising. two windings exactly alike in all respects and wound superimposed one on the U0 other. The two windings of set 11 are designated A and D and the two windings of set 12 are designated B and C. The winding A of set 11 is connected 'to the winding B of set 12 by a conductor 13, and the win in II I), of set 11 is connected to the winding 1m. semi Io. 41,134.

of set 12 by a conductor 14. The other terminals of windings A and C are connecte together by a conductor 15, and the other terminals of windings B and D are con nected together by a conductor 16. Conductors 15 and 16 are connected to. line wires 7 and 8 b conductors 17 and 18. Windings A an B are connected thus in series to line wires 7 and'8 and windings C and D are connected likewise in series to line wires 7 and 8; and windings A, B are in parallel to winding? 0, D. Motor armature 5 is connected y-conductors 19 and 20 to conductors 13 and 14, it bein connected thus bet-ween windings A, B an windings C D. The arrangement of the connections will be clear from the wiring diagram, Fig. 3.

Considering the wiring diagram, it will be clear that when the ratio of the imped-' ance of windin A to the impedance of winding B equa s the ratio of the impedance of winding C to the impedance of winding D, no current will flow througharmature 5 but that when this condit1on does not obtain current will flow through armature 5 in one direction or the other depend- 'ing upon the direction and amount of the unbalance. This is the well-known Wheatstone bridge arran ement.

In connection with the two sets of coils 11 and 12-, I arrange a core structure which provides magnetic circuits for the windin and I thenprovide means for varyin t e reluctance of such magnetic circuits w erebly the rcactance of the windings may be c ianged. The core structure comprises a stationary rectangular yoke 21 formed of suit-able laminations and provided with four inwardly projecting poles 22, 23, 24 and 25. The two sets of coils are arranged in this yoke. In the center of the yoke is a movable plunger 26 formed of suitable laminations and having four poles 27, 28, 29 and 30 which approach oles 22, 23, 24 and 25. Plun r 26 is carrie on one end of a lever 31 in crumed at 32, the other end bein connected to some means for moving the ever, here indicated as a rod 33. By movin lever 31 on its fulcrum the widths of the air gaps between pole faces 22 and 27 and between pole faces 23 and 28 is varied. The faces of pole pieces 27 and 28 are beveled to an extent such that when brought up to the ,faces of pole pieces 22 and 23 they are then parallel to' them. The width of the air gaps between pole faces 24 and 29 and between -.pole faces 25 and 30 remain constant'and are made as small as practical.

In the illustrated embodiment of the invention, the four c ils A, B, C and D are similar in design in every respect, coils A and D being wound su rimposed and coils B and G bein wound superim osed, and they are woun in directions suc that the flux due to each is in a common direction.

' With the above described arrangement, when plunger 26 is exactly in the center of yoke 21, the air gaps between pole pieces 22 and 27 and between pole ieces 23 and 28 are equal, and since all t e windings are similar and are wound in a direction I such that the flux due to each is in a common direction, there will result a magnetic field common to all four windings. This field will travel through yoke 21 and pole pieces 22, 27, 28 and 23, no flux passin through pole pieces 24, 29, 30 and 25. Wit this con-. ition obtaining, the impedance of all the coils A, B, C and D will be the same and no current will flow through motor armature 5. As a result, the motor will be stationary. The design of the windings and core structure is such that under these conditions, i. e.,.

zero potential on armature 5, but a small amount of pplwer will be consumed in the windings. is may be accom lished by designing the structure so that t e power factor, with zero potential on armature 5, is of low value.

If now the lunger 26 is moved to decrease the widt of the air gap between ole pieces 22 and 27 and to increase the width of the air gap between pole pieces 28 and 23 the magnetic circuits will become unbalanced since the reluctance of the magnetic path for windings A, D will have been decreased and that for windings B, C increased. As a result, the flux created by windin s A, D will be increased and that created by Windings B, C will be decreased, the increased flux due to windings A, D through pole pieces 24, 29 and 30, 25. It to lows, therefore, that the reactance of both windings A and D is increased and the reactance of both windings B and C is decreased. The Wheatstone bridge thus becomes unbalanced, whereby a potential will be placedv on motor armature '5 causing it-to rotate in one direction. If plunger 26 is moved in the other direction from its neutral or central position, the same effect takes place except that the unbalancing is in the other direction and the motor armature is caused to run in the other direction. Thus by movin plunger 26 one way from central position t e motor is operated in one direction and by moving p unger 26 the other way from central position, the motor is operated in the other direction, since the field is in a relatively constant direction. The

'ance of windings comparatively small now passin amount of unbalance of the Wheatstone bridge, and hence the value of the potential imposed on motor armature 5, varies in accordance with a direct function of the amount which the plunger 26 is moved. Any motor speed in either direction from a very slowcree ing movement to maximum 8 eed can be c tained by gradually moving t e lunger.

en plunger 26 is moved, the reactance of all four windin s is chan d, the reactand D fling changed in a direction alwa s opposite to that of windings B and C. This means that a maximum increase in the unbalance of the bridge takes place for each increment of movement of the plunger. As a result, the motor may be operated over a wide speed range with a total movement of the plunger.

My improved motor controlling means may be used for motor control wherever it is found applicable. One application, by way of illustration, is .shown in Fig. 4, wherein it is'utilized to adjust the loading spring of a turbine governor in order to regulate the valve-opening of the turbine,

the specific application being m connection with a back pressure governor.

Referring to Fig. 4, 34 indicates an elastic fluid turbine provided with a valve ar 35 which regulates the flow of elastic uid to the turbine. The exhaust conduit of the turbine is indicated at 36 and the shaft of the turbine at 37. The valve gear 35 may be of any suitable type, a known ty being indicated diagrammatically in the rawing.

It is adapted to be moved by a fluid-actuated motor 38, the pilot valve of which is indicated at 39. The fluid-actuated motor is controlled by a spe d governor 40 driven from the shaft of the turbine and connected tot-he fluid-actuated motor b a link 41.- 42 indicates a loading spring ar governor 40, and 43 indicates an alternatin current motor for'varying the tension 0 spring 42 through the worm gearing 43'. The arrangement illustrated is only by way of example, motor 43 representing any electric motor used to regu ate the speed of a turbine. a

My improved'motor controlling device is indicated generally at 44 and is connected to motor 43 in accordance with the wiring arrangement shown in Fig. 1.

The operating rod 33 is connected to a bellows 45, the movement of which is opposed by a spring 46. Bellows 45 is located in a casing 47 and this casing is connected by a pipe 48 to exhaust conduit 36. The bellows 47 is thus subject to the pressure in the ex haust conduit of the turbine. It is set so that when the desired pressure obtains in conduit 36, plunger 26 of the regulating device will be held in its middle position. If,

- accepts.

however, the pressure increases or decreases from this value, the bellows 45 will be either expanded or contracted to move plunger 26 in one direction or the other, thereb efiecting movement of motor 43 in one irection or the other to vs the setting of the governor and hence t e valve-opening of the turbine valve mechanism. A back pressure gpivernor for elastic fluid turbines is well own; Fig. 4 illustrates the application of my improved motor controlling arrangement to such an apparatus.

My motor control mechanism possesses utility not only because of the fact that its operation'requires the opemng and closing 0 no contacts, which means that all contact troubles are eliminated, but also because of its great sensitiveness. The slightest movement of plunger 26 serves to unbalance the Wheatstone bridge and start the motor moving. In actual practice I have demonstrated that with a construction embodyin my invention, a motor may be operated in either direction from a very slow, creeping motion to its maximum speed. A sensitive control of this character is of articular -utility where comparatively fine a justments are required; -I have demonstrated also that by means of my invention, a motor may be operated through its total speed range in both directions with a comparatively small" total m movement of the plunger 26. This mal es the mechanism articular-1y useful in 1nstances, such as i lustrated 1n Fig. 4 for example, wherein it is desired to obtain motor control in response to comparatively small initial movements.

In accordance with the provisions of the patents statutes, I have described the princi le of operation of my invention, together with the ap aratus which I now consider to represent t e best embodiment thereof, but I desire to have it understood that the apparatus shown is only illustrative and that the invention may be carried out by other means.

What I claim as new and desire to secure by Letters Patent of the United States, is

1. The combination with an alternatin current motor, of means for controlling it com rising four windings connected to form a eatstone bridge, means providing magnetic circuits for said windings, and means for varying the reluctance of said magnetic circuits, the motor armature being connected to one pair of the bridge terminals, and the other air of bridge terminals and the motor field being connected to a source of alternating current.

2. The combination with an alternating current motor, of means for controlling it com rising four windings connected to form a eatstone bridge, conductors connecting the motor armature to one pair of the bridge terminals, a source of alternating current,

ings,-and means for varying the reluctance l of said magnetic circuit..

3. The combination with an alternating current motor, of means for controlling it OOIaPIISHIg four windings connected to form a heatstone brid a, two of said windings 7 being superimposc on each other, conductors connectin the motor armature to one pair of the bridge terminals, 0. source of alternating current, conductors connecting the motor field and the other pair of bridge terminals to said source, a structure which provides a magnetic circuit for said superimposed windmgs, and means for varying the reluctance of said magnetic circuit.

4. The combination with an alternatin current motor, of means for controlling it com rising four windings connected to form a W eatstone bridge, the opposite windin of the bridge being superimposed on ea l i other to form two sets of windings, conductors connecting the motor armature to one pair of the bridge terminals, a source of alternating current, conductors connecting the motor field and the other pair of bridge terminals to said source, means providing a a etic c1rcu1t for each set of windin an means for simultaneously varying t e reluctance of said magnetic circuits in opposite directions.

5. The combination with an alternating current motor, of means for controlling it comprising a core structure, two sets of coils thereon, each set comprising two similar superimposed windings], said four windings being connected toget er to form a Wheatstone bridge, conductors connecting the motor armature to one pair of the bridge terminals, a source of alternating current, conductors connecting the motor field and the other pair of bridge terminals to said source, anda movable plunger associated with said core for varying the reluctance of the magnetic circuits of said windings.

6. The combination with an alternatin current motor, of means for controlling it com rising a rectangular core having inwar ly projecting pole pieces, two' sets of coils thereon, each set comprising two similar superimposed windings, said four windings being connected to ether to form a Wheatstone bridge, cond the motor armature to one pair of the bridge terminals, a source of alternating current, conductors connecting the motor field and the other air of bridge terminals to said source, and a plunger inside the core and movable relatively to its pole pieces for varyin the reluctance of the magnetic circuits o said windings.

7.-"The combination with an alternating uctors connecting current motor having, a field member'and an armature member, of means for controlling the motor comprising four windings connected to form a Wheatstone bridge, conductors connecting one of the motor members to one pair of the bridge terminals, 11 source of alternating current, conductors connecting the other motor member and the other pair of bridge terminals to said source, a structure which provides a magnetic circuit for at 10 least one of said windings, and means for varying the reluctance of said magnetic circuit.

In witness whereof, I have hereunto set my hand this 28th day of July, 1925.

REGINALD G. STANDERWICK. 

